This section provides background information related to the present disclosure which is not necessarily prior art. The present disclosure relates to conductive metal coatings on porous filler materials. The disclosure describes the methods for making such filler materials and using such materials in electrical and/or thermal applications.
Enhancement of electrical and thermal conductivities of composite material requires suitable fillers with high filler loadings. Typical fillers used for making conductive articles include metals, metallic salts (e.g., aluminum salts, etc.), ceramics (e.g., calcium salts, aluminum nitride, boron nitride, calcium phosphates, hydroxyapatite, calcium carbonates, calcium sulfates, combinations thereof, etc.) and carbon (e.g., carbon fibers, graphite, carbon black in various forms ranging from nano to micrometer size range, etc.). The main objective in the field of electrically conductive and thermally conductive article manufacture is to obtain desired property values with minimum amounts of fillers. High electrical and thermal conductive values require higher amount of filler loading. Fillers have different densities, which therefore results in segregation (especially of higher densities). In view of this, uniform distribution of fillers is difficult to achieve. An inhomogeneous distribution of fillers will lead to poor and inconsistent properties.
High loading of fillers is difficult to achieve in view of enhanced viscosities during processing such as injection molding. Further, differences in densities lead to segregation resulting in heterogeneity. Traditionally, metallic coatings such as silver or nickel are applied on to the surface of glass beads or polystyrene balls to reduce the cost of fillers. Though this may provide higher conductivity at a lower cost, a small discontinuity will result in failure of conducting path.
The separation at the interface between metal and host particles presents significant challenges in the manufacture of metallized filler or carrier particles. Since the filler particles and the metal to be coated thereon have different interfacial properties, the metal will likely separate from the filler particles due to changes with time or environmental changes (especially temperature changes and shear during processing), resulting in a reduced conductivity.
In order to prevent powder particle-metal separation and produce powder particles having a metal coating closely adhered thereto, others in the field have tried to ameliorate the above stated problems by producing filler particles that are etched to introduce irregularities in their surface to increase the surface area thereby improve the metal adhesion. Powder particles have also been treated with a silane coupling agent such as a monomeric silane, typically gamma-aminopropyltriethoxysilane for improving the metal adhesion. Powder particles have also been treated with an organic resin such as an epoxy resin for improving the metal adhesion.